Slow Strain Rate Tensile Properties of X80 Pipeline Steel in Different Hydrogen-Containing Environments

Slow strain rate tensile tests were carried out on base metal axial and circumferential specimens and weld specimens of X80 pipeline steel in 12 MPa high pressure environment with gas composition (volume fraction) of 2% H₂+2% CO₂+N₂ (2% hydrogen environment), 5% H₂+2% CO₂+N₂ (5% hydrogen environment) and 100% N₂ (hydrogen-free environment). The tensile properties of specimens in different environments were studied, and the hydrogen embrittlement sensitivity of base metal and weld was evaluated based on the percentage reduction of area. The results show that compared with those in the hydrogen-fee environment, the percentage elongation after fracture of the base metal axial specimen in 2% hydrogen environment and 5% hydrogen environment decreased by about 1% and 5%, of the base metal circumferential specimen decreased by about 7% and 11%, and of the weld decreased by about 7% and 12%, respectively. The plasticity deterioration degree of the weld was greater than that of the base metal, with a greater degradation in the 5% hydrogen environment. The tensile strengths of base metal and weld in 2% and 5% hydrogen environments were basically similar. In the same hydrogen-containing environment, the tensile strength of the base metal circumferential specimen was higher than that of the axial specimen, and the tensile strength of the weld was the lowest; the plasticity of the base metal axial specimen was better than that of the radial specimen, and the plasticity of the weld was the worst. The hydrogen embrittlement sensitivities of base metal and weld in 2% hydrogen environment were lower than that in 5% hydrogen environment. The hydrogen embrittlement sensitivity of weld was the largest, followed by base metal circumferential specimen and axial specimen in the same hydrogen-containing environment.